1. Field of the Invention
The invention relates to the field of hinge assemblies for coupling two structures together and for rotating one structure from an over lapping position with the other structure to an in line position therewith and, in particular, to a hinge assembly for extending fragile structures such as solar panels on a satellite in orbit wherein excess rotational energy is absorbed reducing stress loads on the structures.
2. Description of Related art
The cost of putting a satellite in orbit increases in proportion to its weight and size. Thus such satellites are constructed of light weight materials with small margins of safety on strength. Therefore, the solar panels that provide power once in orbit are stored in a folded position until orbit is reached. In addition, they are designed from a strength standpoint for deployment only after orbit is reached. When deploying such fragile structures in orbit, great care must be taken to insure that the loads induced on the individual panels as they are unfolded will not cause damage thereto. In particular, the sudden deceleration forces of the panels as they reach the unfolded in line position can cause over stressing of the individual panels, especially if the panels are caused to oscillate as they reach the in line position. If the damage is significant, complete failure of the satellite may occur.
This problem has long been recognized. For example, U.S. Pat. No. 4,561,614 "Deployable Folded Multi-Element Satellite Subsystems" by P. Olikara, et al. discloses a spring biased hinge incorporating viscous fluid dampers to absorb or dampen such forces. Each of the dampers includes a heater and thermostat to maintain the same damper temperature in each hinge assembly to insure that all the panels unfold at the same rate. However, such a system is complicated and heavy. It may also not provide the high reliability required in modern satellite systems.
U.S. Pat. No. 5,356,095 "Attenuating Linked Deployment Apparatus" by G. I. Aker discloses a hinge assembly wherein the hinge members are biased to the open or inline position by a coil (torsional) spring mounted on the hinge axis. One of the hinges has a "projecting lobe portion" having a surface that is adapted to contact a load attenuator mounted on the other hinge member. Contact occurs just prior to the hinge members reaching the in line position, thus damping out any oscillatory forces. A cam locking system is included that locks the projecting lobe portion in place, and thus the hinge member, when the hinge member reaches the in line position or unfolded (deployed) position. While this design should offer increased reliability over the P. Olikara, et al. design, a separate locking system adds weight and may jam, preventing full deployment of the hinge members.
Thus, it is a primary object of the invention to provide a hinge assembly is suitable for unfolding fragile structures such as solar panels on satellites in orbit.
It is another primary object of the invention to provide a hinge assembly that reduces the shock loads upon the hinge members reaching the in line position.
It is a further object of the invention to provide a hinge assembly that automatically locks when reaching the in line position.